Method for manufacturing a supporting plate for a filter

ABSTRACT

A method for manufacturing a supporting plate provided inside of a disc-type filter having filter media at surface portions thereof including the steps of: forming an annular plate having opposed surfaces; and 
     forming a plurality of wave portions on the annular plate that alternately extend beyond the opposed surfaces in opposite directions by pressing, each of the plurality of wave portions extending substantially in a circumferential direction of the annular plate and the plurality of wave portions being arranged substantially adjacent to each other in a radial direction of the annular plate. 
     The supporting plate has high pressure resistance, low-pressure loss property, good directivity of polymer flow and excellent polymer mixing effect, and it is suitable for use as retainer disposed inside of a filter.

This application is a divisional of application Ser. No. 08/408,483,filed Mar. 22, 1995 which is now U.S. Pat. No. 5,611,925.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hub ring and a supporting plate for afilter and methods for manufacturing these members.

2. Description of the Related Art

Disc-type filters are known as filters for filtering a polymer, and forexample, a so-called leaf disc-type filter and a three-layer type filterwherein disc-type filter materials are disposed on and under a retainerfor forming a single filter element are well known. Such filters areusually used by stacking a plurality of filter elements by a numbercorresponding to a capacity of filtration to be required (flow rate of amolten polymer to be filtered). In the case of use of stacked filters,because it is necessary to seal a polymer after filtration from apolymer before filtration, a hub ring is provided on the innercircumference of each filter (as needed, it may be provided on the outercircumference of each filter). Such a hub ring seals polymers after andbefore filtration from each other and ensures a path for the polymerafter filtration, as described above, as well as maintaining apositional relationship between respective stacked filters (for example,interval of filters).

As a typical structure of conventional filters, for example, a structureshown in FIG. 22 is known. FIG. 22 illustrates a part of an innercircumferential portion of a leaf disc-type filter 101. A filter medium104 is provided on each side of a retainer 102 constructed from, forexample, a mesh, via a filter medium supporting material 103 constructedfrom a perforated plate (for example, a punching metal). A hub ring 105is provided on the circumference of filter 101, and a plurality of smallholes 106 are provided in the hub ring 105. A molten polymer 107 flowsinto filter media 104 from upper and lower sides, and the polymer 107filtered by the filter media 104 passes through a portion of retainer102 and holes 106 of hub ring 105 to be gathered a central portion, asshown by the arrows in FIG. 22.

In a case where a plurality of filters 101 are stacked, a predeterminednumber of filters 101 are fitted and stacked around a tubular supportingpole 108, and the gap between filter media 104 of adjacent filters 101is set based on the dimension of the portion of hub ring 105. Respectivehub rings 105 of stacked filters 101 are pressed from upper or lowerside by a great fastening pressure capable of sealing polymers after andbefore filtration from each other, for example, a pressure of 5-10 tons.

In such a conventional structure, there remain the following problems.

Firstly, although a number of small holes 106 are opened in hub ring 105for passing a polymer after filtration, the opening ratio thereof isabout 20% at highest, and the small opening ratio causes a largepressure loss generated at this portion. Although it may be consideredto enlarge the diameter of the holes in order to increase the openingratio, the enlargement of the hole diameter is restricted to some extentby the above-described great fastening pressure.

Moreover, in the above structure defining small holes, in the upstreamside of the polymer flow, the portions around the small holes 106 arelikely to create a large dead space against the polymer flow. Such adead space causes residence of polymer, and the residence of polymercauses degradation of the polymer and flowing-out of the degradedpolymer, and therefore it is desired to suppress such a dead space assmall as possible.

Furthermore, since the small holes 106 must be processed in the radialdirection of hub ring 105, the processing is relatively difficult and along time is required for the processing. Therefore, the cost formanufacturing the hub ring 105 is relatively expensive.

Still further, for the retainer 102, a relatively high strengthparticularly against deformation of the retainer in the thicknessdirection thereof, for example, a pressure resistance of about or higherthan 200 kg/cm², is usually required in order to maintain the form ofthe filter to an acceptable form and in order to ensure the polymer pathin the radial direction of the filter at the position of the retainer.Even by the mesh type retainer 102, such a high strength for a highpressure resistance can be satisfied. In the mesh type retainer 102,however, particularly there are the following problems with respect topressure loss and polymer residence.

Namely, in the mesh type retainer 102, because wires extending in thecircumferential direction of the filter while waving (usually, the wirehas a diameter corresponding to 1/2 of the thickness of the retainer 102or a diameter slightly greater than that value) cause a large resistanceagainst the polymer flow in the radial direction of the filter, it isdifficult to suppress the pressure loss at the portion of the retainer102, ultimately the pressure loss of the whole of the filter 101, to asmall value.

Further, in the portion of the retainer 102, the polymer flows towardradially inner direction mainly along the wires extending in the radialdirection of the filter. These wires extending in the radial directionof the filter form a dead volume against a polymer path rather thanforming a polymer path, and therefore, the polymer flow has a poordirectivity in the radial direction of the filter and it may bedifficult to achieve a smooth polymer flow. The difficulty of a smoothpolymer flow causes a poor chance of polymer mixing. Therefore, there isa latent problem that the polymer mixing effect (also called "staticmixer effect") is small. Furthermore, there is a fear causing a problemof polymer residence. Also with the wires extending in thecircumferential direction of the filter, there are similar problemsbecause they form a dead volume against the polymer flow.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a hub ring for a filterwhich can achieve a great opening ratio of a polymer path and anextremely low pressure loss, which hardly causes residence of polymerand which can be manufactured easily and inexpensively, and a method formanufacturing the same.

Another object of the present invention is to provide a supporting platefor a filter which has a high pressure resistance and can be easilyformed as a shape causing a low pressure loss, which can easily providea desired directivity to a polymer flow without causing residence of thepolymer flow as well as can realize an excellent polymer mixing effect,and which is suitable for use as a retainer provided inside of a filterelement, and a method for manufacturing the same.

A further object of the present invention is to realize a furtherlow-pressure loss, high-pressure resistance and high-quality filter bycombining the above-described hub ring and supporting plate.

To accomplish these objects, a hub ring according to the presentinvention is provided on at least one of inner and outer circumferencesof a disc-type filter. The hub ring comprises: (a) a pair of keep platesdisposed spacedly from each other and in parallel to each other, each ofthe pair of keep plates being formed as an annular plate; and (b) anannular supporting member disposed between the pair of keep plates. Thesupporting member has (i) a plurality of supporting portions disposedspacedly from each other in a circumferential direction of the hub ring,each of the plurality of supporting portions extending between the pairof keep plates in a direction substantially perpendicular to the pair ofkeep plates and extending in a radial direction of the hub ring and (ii)an annular plate portion connected to the plurality of supportingportions.

The annular plate portion of the annular supporting member may beconnected to one of the inner and outer sides of the plurality ofsupporting portions in a radial direction of the hub ring formaintaining a desired arrangement of the plurality of supportingportions.

A method for manufacturing a hub ring according to the present inventionis herein provided. The hub ring is provided on at least one of innerand outer circumferences of a disc-type filter. The method comprises thesteps of:

(a) defining a plurality of slits on an annular plate at a position ofone of inner and outer circumferential sides of the annular plate, theplurality of slits being arranged over the entire length of one of innerand outer circumferential sides of the annular plate, each of theplurality of slits extending in a radial direction of the annular plate;

(b) twisting portions positioned between respective adjacent slitssubstantially at an angle of 90 degrees relative to the annular platefor making an annular supporting member; and

(c) disposing a pair of keep plates on and under the twisted portions ofthe annular supporting member, each of the pair of keep plates beingformed as an annular plate.

Further, a method for manufacturing a hub ring for a filter according tothe present invention comprises the steps of:

(a) defining a plurality of straight slits one side of the plate, theplurality of slits being arranged substantially over the entire lengthof the plate, each of the plurality of slits extending in a widthdirection of the plate;

(b) twisting portions positioned between respective adjacent slits andend portions positioned outside of both end slits substantially at anangle of 90 degrees relative to the plate;

(c) forming an annular supporting member by rounding the plate so as toarrange the twisted portions along one of inner and outer circumferencesof the annular supporting member; and

(d) disposing a pair of keep plates on and under the twisted portions ofthe annular supporting member, each of the pair of keep plates beingformed as an annular plate.

Thus, the plurality of supporting portions are easily formed by twistingportions positioned between respective adjacent slits at an angle of 90degrees. In order to easily perform this twisting and in order toprovide a great pressure resistance to the formed supporting portions ata position between a pair of keep plates, the material of the annularsupporting member is desired to be constructed from a stainless steel.

In such a hub ring for a filter, since a number of supporting portionsextending substantially perpendicularly to a pair of keep plates areinterposed between the pair of keep plates, spaces defined betweenrespective adjacent supporting portions are formed as polymer paths fora polymer after filtration which extend in the radial direction of thefilter. Further, in the area between a pair of keep plates, all theportions other than the supporting portions function a polymer path.Therefore, the opening ratio of the polymer path can be greatlyincreased as compared with the conventional structure provided withsmall holes and having a large dead space, and thereby greatlydecreasing the pressure loss.

Further, the supporting portions extend substantially perpendicularly toa pair of keep plates and function as shorings against a compressionload applied to the pair of keep plates. Therefore, they can indicate anextremely great pressure resistance as compared with a conventionalmember having waving wires, as long as buckling does not occur in thesupporting portions. Because the dimension between the pair of keepplates is usually small and it is about 5 mm at largest, buckling doesnot occur in the supporting portions. As a result, even if a greatcompression load is applied to the pair of keep plates, that is, even ifa fastening force is applied to respective hub rings in a filterstacking structure, each hub ring is not deformed and theabove-described polymer path having a great opening ratio can bemaintained in a desired condition with no trouble.

The annular plate portion is positioned at the inner circumferentialside or outer circumferential side of the annularly arranged supportingportions. In this portion of the annular plate portion, the whole of thespace between a pair of keep plates functions as a polymer path.Therefore, also in this portion, a great opening ratio of a polymer pathis ensured, and the pressure loss can be suppressed.

Thus, the pressure loss can be extremely suppressed as the whole of thehub ring by the large opening ratio, and there is no portion causingresidence of polymer in the polymer path in the hub ring and the wholeof the polymer after filtration can pass smoothly through the hub ring.

Further, in the hub ring according to the present invention, a pair ofkeep plates each formed as an annular plate and the annular supportingmember having supporting portions and an annular plate portion can beseparately manufactured. The pair of keep plates can be easily made, andeven the supporting member, as aforementioned, can be easily made bydefining a plurality of slits extending in the radial direction on anannular plate at a position of one of the inner and outercircumferential sides of the annular plate and twisting portions betweenrespective adjacent slits at an angle of 90 degrees. Further, the keepplates and the supporting member can be integrally formed, for example,by welding these members, thereby making a hub ring excellent inhandling. Thus, not only respective members constituting a hub ring butalso the hub ring itself can be manufactured extremely easily, and alarge number of hub rings can be manufactured in a short period of timeas well as the cost for manufacture can be greatly reduced as comparedwith that for the conventional hub rings.

A supporting plate for a filter according to the present invention isprovided inside of a disc-type filter having filter media at surfaceportions thereof. The supporting plate comprises a plurality of waveportions each extending substantially in a circumferential direction ofthe filter and waving in a thickness direction of the filter. Theplurality of wave portions are formed by pressing so as to be arrangedsubstantially adjacent to each other in a radial direction of thefilter.

In the supporting plate, a portion present between two wave portionsadjacent to each other in the direction of said filter may remain as aportion which does not wave.

The form of each wave portion is not particularly restricted. Forexample, wave forms of two wave portions adjacent to each other amongthe plurality of wave portions may shift substantially by a 1/2 pitch ofone of the wave forms in a circumferential direction of the filter, andmay shift by 1/3 or 1/4 pitch.

The wave forms of the plurality of wave portions may have substantiallya constant pitch over the entire area in which the plurality of waveportions are formed. Alternatively, a pitch of a wave portion formed ata radially outer position and a pitch of a wave portion formed at aradially inner position may be different from each other. For example, apitch in a radially inner portion may be smaller than a pitch in aradially outer portion or the pitch may be set so as to become graduallysmall toward the radially inner direction, or on the contrary, the pitchmay be set so as to become gradually large toward the radially innerdirection. The pitch of the wave forms is not particularly restricted,and it may be appropriately designed in accordance with, for example, awidth of a single wave portion, easiness of pressing for forming thewave portions, or thickness and material of a annular plate prepared asa raw material plate for manufacturing a supporting plate to be pressedto wave portions.

For example, in a case where the raw material plate is a stainless steelhaving a thickness of 0.3 to 1.2 mm, the width of a single wave portionis preferably in the range of 0.5 to 4.0 mm, more preferably in therange of 1.0 to 3.0 mm, and the pitch of the wave form is preferably inthe range of 2.0 to 8.0 mm, more preferably in the range of 3.0 to 6.0mm.

The pattern for the wave portions can be freely designed as long as theabove-described conditions are satisfied.

For example, the following structure can be employed. A first group ofwave portions extending substantially straight in the circumferentialdirection of the filter at a constant angle relative to a radialdirection of the filter within a first region of the supporting platecircumferentially divided at a predetermined circumferential angle, anda second group of wave portions extending substantially straight in thecircumferential direction of the filter at the same angle as theconstant angle relative to a radial direction of the filter within asecond region of the supporting plate circumferentially divided at apredetermined circumferential angle which is adjacent to the firstregion in the circumferential direction of the filter.

Alternatively, the following structure can be employed. A first group ofwave portions extending substantially straight in the circumferentialdirection of the filter at a constant angle relative to a radialdirection of the filter within a first region of the supporting platecircumferentially divided at a predetermined circumferential angle, anda second group of wave portions extending substantially straight in thecircumferential direction of the filter at an angle different from theconstant angle relative to a radial direction of the filter within asecond region of the supporting plate circumferentially divided at apredetermined circumferential angle which is adjacent to the firstregion in the circumferential direction of the filter.

Further, a structure, wherein the plurality of wave portions extendconcentrically in the circumferential direction of the filter, can alsobe employed.

Furthermore, although it is preferred that the supporting plate isconstructed as an integrally formed single annular member, it may beconstructed from a plurality of members divided in the circumferentialdirection of the filter.

Although the material of the supporting plate is not particularlyrestricted as long as it is made from a metal capable of being pressed,particularly a stainless steel is preferred. By pressing a raw materialof a stainless steel, work hardening can occur on the formed waveportions, thereby further increasing the pressure resistance thereof.Moreover, a stainless steel is preferred from the viewpoint ofrustproofing. Although the wave portions can have a sufficiently highstrength only by press forming even if there is a slight residualstress, it may be subjected to annealing at a low temperature afterpress forming in order to ensure a further high pressure resistance asneeded. In the case of stainless steel, the low temperature annealing isperformed preferably at a temperature of 410° to 440° C. Further, aprecipitation hardening type stainless steel may be employed in order toincrease the strength.

Another supporting plate for a filter according to the present inventioncomprises a base plate portion formed as an annular plate; and aplurality of riser piece portions disposed in radial and circumferentialdirections of the base plate portion. Each of the plurality of riserpiece portions extends in a radial direction of the base plate portionand rises from upper and lower surfaces of the base plate portion in adirection perpendicular to the base plate portion by being twistedsubstantially at an angle of 90 degrees relative to the base plateportion.

In this supporting plate, in a case where the plurality of riser pieceportions are disposed concentrically on the base plate portion and aring portion of the base plate portion is formed at a position betweenradially adjacent rows of riser piece portions, the ring portion ispreferably waved in a thickness direction of the base plate portion. Inthis case, it is preferred that the heights of the riser piece portionsfrom the upper and lower surfaces of the base plate portion aresubstantially the same as the heights of a wave form of the ring portionfrom the upper and lower surfaces of the base plate portion. Further,this type of supporting plate is preferably constructed from a stainlesssteel.

The above-described supporting plates for a filter according to thepresent invention are disposed inside of a disc-type filter havingfilter media at both surfaces portions thereof, and can be used as aretainer which is a substitute for the retainer shown in FIG. 22 or as afilter media supporting and retainer material.

For example, in a case where a filter comprises filter media at surfaceportions, filter media supporting material positioned inside of thefilter media and a retainer at an innermost position, the retainer maybe constructed by the supporting plate according to the presentinvention. Alternatively, in a case where a filter comprises filtermedia at surface portions and a filter media supporting and retainermaterial disposed inside of the filter, this filter media supporting andretainer material may be constructed by the supporting plate accordingto the present invention.

Further, the supporting plate according to the present invention can beapplied together with the aforementioned specified hub ring for a filterwhich can realize a large opening ratio of a polymer path and aextremely low pressure loss, in which residence of polymer hardly occursand which can be manufactured easily and inexpensively. By thiscombination, a filter having properties of further low pressure loss,high pressure resistance and high performance can be realized.

Namely, in an assembly of a supporting plate and a hub ring for a filteraccording to the present invention, a supporting plate is providedinside of a disc-type filter having filter media at surface portionsthereof and a hub ring is provided on at least one of inner and outercircumferences of the disc-type filter. The assembly is characterized inthat the supporting plate comprises a plurality of wave portions eachextending substantially in a circumferential direction of the filter andwaving in a thickness direction of the filter, the plurality of waveportions being formed by pressing so as to be arranged substantiallyadjacent to each other in a radial direction of the filter, and the hubring comprises:

(a) a pair of keep plates disposed spacedly from each other and inparallel to each other, each of the pair of keep plates being formed asan annular plate; and

(b) an annular supporting member disposed between the pair of keepplates, the supporting member having (i) a plurality of supportingportions disposed spacedly from each other in a circumferentialdirection of the hub ring, each of the plurality of supporting portionsextending between the pair of keep plates in a direction substantiallyperpendicular to the pair of keep plates and extending in a radialdirection of the hub ring and (ii) an annular plate portion connected tothe plurality of supporting portions.

Another assembly of a supporting plate and a hub ring for a filteraccording to the present invention is characterized in that thesupporting plate comprises:

a base plate portion formed as an annular plate; and

a plurality of riser piece portions disposed in radial andcircumferential directions of the base plate portion, each of theplurality of riser piece portions extending in a radial direction of thebase plate portion and rising from upper and lower surfaces of the baseplate portion in a direction perpendicular to the base plate portion bybeing twisted substantially at an angle of 90 degrees relative to thebase plate portion, and the hub ring comprises:

(a) a pair of keep plates disposed spacedly from each other and inparallel to each other, each of the pair of keep plates being formed asan annular plate; and

(b) an annular supporting member disposed between the pair of keepplates, the supporting member having (i) a plurality of supportingportions disposed spacedly from each other in a circumferentialdirection of the hub ring, each of the plurality of supporting portionsextending between the pair of keep plates in a direction substantiallyperpendicular to the pair of keep plates and extending in a radialdirection of the hub ring and (ii) an annular plate portion connected tothe plurality of supporting portions.

In both the assemblies, the annular supporting member can be formedintegrally with the supporting plate. However, the supporting plate andthe hub ring may be formed separately, and both members may be appliedtogether.

A method for manufacturing a supporting plate provided inside of adisc-type filter having filter media at surface portions thereof,according to the present invention, comprises the steps of preparing anannular plate; and forming a plurality of wave portions on the annularplate by pressing, each of the plurality of wave portions extendingsubstantially in a circumferential direction of the annular plate andwaving in a thickness direction of the annular plate, the plurality ofwave portions being arranged substantially adjacent to each other in aradial direction of the annular plate.

In this method, a first group of wave portions is formed by pressing ona first region of the annular plate circumferentially divided at apredetermined circumferential angle. Then a second group of waveportions is formed by pressing on a second region of the annular plateadjacent to the first region in the same pattern as that in the firstregion, and by repeating these operations of pressing, a plurality ofwave portions are formed substantially over the entire circumference ofthe annular plate. Alternatively, the plurality of wave portions areformed by pressing, using a plurality of annular dies having diametersdifferent from each other. Further, although the above-described waveportions can be formed only by pressing, a method may be employedwherein a plurality of slits are defined intermittently in thecircumferential and radial directions of the annular plate, and portionsbetween respective pairs of slits are formed as the wave portions bypressing.

Another method for manufacturing a supporting plate provided inside of adisc-type filter having filter media at surface portions thereof,according to the present invention, comprises the steps of defining aplurality of slits or slots on an annular plate, each of the pluralityof slits or slots extending in a radial direction of the annular plate,the plurality of slits or slots being disposed in the circumferentialdirection of the annular plate as well as disposed in the radialdirection of the annular plate in forms of a plurality of annular rows;and forming a plurality of riser piece portions rising from upper andlower surfaces of a base plate portion of the annular plate in adirection perpendicular to the base plate portion by twisting respectiveportions present between respective pairs of the slits or slotssubstantially at an angle of 90 degrees relative to the base plateportion.

In this method, it is preferred that each of the slots is formed as aslot having circular holes at both end portions in its longitudinaldirection and the circular holes have a diameter greater than a width ofa central portion of the slot.

In the above-described supporting plate wherein a plurality of waveportions each extending substantially in a circumferential direction ofthe filter and waving in a thickness direction of the filter and theplurality of wave portions are formed by pressing so as to be arrangedsubstantially adjacent to each other in a radial direction of thefilter, because the wave portions are formed by pressing, adjacent waveportions are connected to each other via original raw material (anannular plate) at any portion. Therefore, even if a plurality of waveportions are disposed so as to be adjacent to each other, the supportingplate can be maintained as a form of a single plate. Since the waveportions have a waving structure in the thickness direction of thefilter and a plurality of wave portions having the waving structure arearranged adjacent to each other, fluid paths extending in the radialdirection of the filter are formed by the waving structure portionsdisposed adjacent to each other.

For example, in a case where wave forms of two wave portions adjacent toeach other shift substantially by a 1/2 pitch of one of the wave formsin a circumferential direction of the filter, a concave portion of awave form of one wave portion is positioned at a position correspondingto a convex portion of a wave form of the other wave portion locatedradially adjacent, and a convex portion of a wave form of one waveportion is positioned at a position corresponding to a concave portionof a wave form of the other wave portion located radially adjacent. Asviewed in the radial direction of the filter with respect to a pluralityof wave portions, the convex portions and the concave portions arealternately positioned. As a result, the convex portions and the concaveportions adjacent to each other can form a pipe-like fluid path. Sincethis pipe-like fluid path extends in the radial direction of the filter,only by forming a plurality of wave portions by pressing, can aplurality of fluid paths extending radially in the radial direction ofthe filter be formed efficiently.

Further, in a case where wave forms of two wave portions adjacent toeach other shift by 1/3 or 1/4 pitch of one of the wave forms in acircumferential direction of the filter, the fluid paths are formed in acondition where concave portions and convex portions of the respectivewave forms of the plurality of wave portions are offset from each otherin the circumferential direction of the filter. In such a structure, theplurality of fluid paths extending radially in the radial direction ofthe filter are formed as fluid paths being complicatedly bent or beingcomplicatedly communicated with each other, and an excellent fluidmixing effect can be expected.

Since the fluid paths as described above are formed by providing convexand concave portions to an annular raw material plate by pressing, anobstruction against the flow in the radial direction of the filter iscaused only by the portions having the thickness of the plate.Therefore, a large obstruction such as that due to wires in theconventional structure does not occur, and the pressure loss of thefluid flow in the radial direction can be suppressed.

Further, the convex portions of the plurality of wave portions disposedadjacent to each other are arranged in a pattern of a staggered form.The convex portions arranged in such a staggered form can indicate anextremely high resistance against a pressure applied to upper and lowersurfaces of the supporting plate. Therefore, the supporting plate for afilter according to the present invention can have an extremely highpressure resistance.

Furthermore, the fluid paths radially extending, which are formed adescribed above, communicate with each other, and the fluid can freelyflow between adjacent fluid paths. As a result, naturally an extremelyexcellent static mixer effect can be obtained, and a uniformly mixedfluid flows in the radial direction of the filter and is gathered.

By applying such a supporting plate for a filter according to thepresent invention as a retainer provided inside of a filter element or afilter media supporting and retainer material, a filter having anexcellent polymer mixing effect and indicating a low pressure loss and ahigh pressure resistance can be realized.

Further, a more high-performance filter can be obtained by combiningsuch a supporting plate according to the present invention with theaforementioned specified structure of a hub ring.

Furthermore, in a type of supporting plate for a filter wherein aplurality of riser piece portions are disposed in radial andcircumferential directions of a base plate portion, each of theplurality of riser piece portions extend in a radial direction of thebase plate portion and rise from upper and lower surfaces of the baseplate portion in a direction perpendicular to the base plate portion bybeing twisted substantially at an angle of 90 degrees relative to thebase plate portion, the riser piece portions indicate substantially thesame function as that of the wave portions of the above-describedsupporting plate. Therefore, also in this type of supporting plate, afilter having an excellent fluid mixing effect and indicating a lowpressure loss against a radial flow and a high pressure resistanceagainst a pressure applied from upper and lower sides can be realized.

Further objects, features, and advantages of the present invention willbe understood from the detailed description of the preferred embodimentsof the present invention with reference to the appropriate figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Some preferred exemplary embodiments of the invention will now bedescribed with reference to the appropriate figures, which are given byway of example only, and are not intended to limit the presentinvention.

FIG. 1 is a partial perspective view of a filter using a hub ringaccording to an embodiment of the present invention.

FIG. 2 is an elevational view of the hub ring shown in FIG. 1.

FIG. 3 is an enlarged, partial perspective view of the filter shown inFIG. 1.

FIG. 4 is a plan view of an annular supporting member of the hub ringshown in FIG. 1.

FIG. 5 is an enlarged, partial perspective view of the supporting membershown in FIG. 4.

FIG. 6 is a plan view of the supporting member shown in FIG. 4, showinga state during processing.

FIG. 7 is a partial perspective view of a hub ring according to anotherembodiment of the present invention.

FIG. 8 is a plan view of a raw material showing a method for processinga supporting member different from the method shown in FIG. 6.

FIG. 9 is a plan view of a supporting member in which an annular plateportion is positioned at the inner circumference side of a supportingportion arrangement.

FIG. 10 is a partial, vertical sectional view of a filter apparatususing a supporting plate for a filter according to an embodiment of thepresent invention.

FIG. 11 is a partial plan view of a supporting plate according to thepresent invention, showing an example of a pattern of wave portions.

FIG. 12 is a partial perspective view of the wave portions.

FIG. 13 is a partial plan view of a supporting plate according to thepresent invention, showing another example of a pattern of waveportions.

FIG. 14 is a partial plan view of a supporting plate according to thepresent invention, showing a further example of a pattern of waveportions.

FIG. 15 is a partial plan view of a supporting plate according to thepresent invention, showing a still further example of a pattern of waveportions.

FIG. 16 is a partial perspective view of a supporting plate whereinportions which are not formed as wave forms remain between waveportions.

FIG. 17 is a partial, vertical sectional view of a filter element usinga supporting plate according to the present invention as a filter mediasupporting and retainer material.

FIG. 18 is a partial perspective view of a filter element combiningsupporting plate and hub ring according to the present invention.

FIG. 19 is a partial plan view of integrally formed supporting plate andhub ring according to the present invention.

FIG. 20 is a partial plan view of an annular plate for manufacturing asupporting plate for a filter according to another embodiment of thepresent invention.

FIG. 21 is a partial perspective view of a supporting plate for a filtermanufactured from the member shown in FIG. 20.

FIG. 22 is a partial perspective view of a conventional filter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Firstly, preferred embodiments of hub rings for a filter according tothe present invention will be explained with reference to the drawings.

FIGS. 1 to 5 show a hub ring for a filter according to an embodiment ofthe present invention. In FIGS. 1 to 3, label 1 shows the whole of aleaf disc-type filter, and the figures show a hub ring 2 and thevicinity. Filter 1 comprises a retainer 3 disposed in the centralportion in the thickness direction, perforated plates 4 disposed on bothsurfaces of retainer 3, filter media 5 disposed outside of bothperforated plates 4 and hub ring 2 disposed on the inner circumferenceof filter 1. In a case where a predetermined number of filters 1 arestacked, in order to define a predetermined gap (polymer path) betweenrespective filters 1, in this embodiment, spacers 6 each having apredetermined thickness and constructed as a ring member are disposedbetween respective hub rings 2. As shown by arrows, a molten polymer 7to be filtered passes through perforated plates 4 and retainer 3 afterfiltered by filter media 5, and after passes through hub ring 2, it isgathered into a supporting pole 8 disposed at the central position ofstacked filters 1. The gathered polymer is sent to a next process. Inthis embodiment, although spacer 6 is made as a member separate from hubring 2, it may be formed integrally with hub ring 2. Further, thestructure of the hub ring according to the present invention can beapplied to a structure wherein a hub ring is disposed on the outercircumference of a filter.

Hub ring 2 comprises a pair of keep plates 9a and 9b disposed spacedlyfrom each other and in parallel to each other each of which is formed asan annular plate, and an annular supporting member 10 disposed betweenthe pair of keep plates 9a and 9b. In supporting member 10, also asshown in FIGS. 4 and 5, a plurality of supporting portions 10a aredisposed spacedly from each other in a circumferential direction of hubring 2, each of the plurality of supporting portions 10a extends betweenthe pair of keep plates 9a and 9b in a direction substantiallyperpendicular to the pair of keep plates 9a and 9b and extends in aradial direction of the hub ring 2. The plurality of supporting portions10a are connected to an annular plate portion 10b at a position ofradially outer side of the hub ring 2.

The above-described plurality of supporting portions 10a can be formed,for example, by the following method.

As shown in FIG. 6, a plurality of slits 12 extending in a radialdirection are defined at a predetermined pitch on the innercircumferential portion of an annular plate 11 having a predeterminedthickness and prepared as a raw material plate, and portions 13positioned between respective slits 12 are twisted at an angle of 90degrees in the same direction bv using an appropriate jig (not shown).At that time, an annular portion 14 in which slits are not defined arepositioned just at a central portion of the portion 13 twisted at anangle of 90 degrees. By this, the respective portions 13 twisted at anangle of 90 degrees are adjusted at a same level relative to the annularportion 14. These portions 13 twisted at an angle of 90 degrees form theabove-described plurality of supporting portions 10a and the annularportion 14 in which slits are not defined forms the above-describedannular plate portion 10b.

Such a processing can be easily performed, for example, by constitutingthe annular plate 11 prepared as a raw material plate from stainlesssteel having a thickness of about 1 mm. In stainless steel, generallywork hardening can be expected and, therefore, a great stiffness againstbending and buckling caused by a compressed load can be provided to thesupporting portions 10a formed by being twisted at an angle of 90degrees. In particular, if the member is constructed from a cold-rolledstainless steel such as "CSPH" material, great work hardening can beexpected and an extremely great stiffness can be provided. In such astainless steel, even if the thickness of the plate is about 0.6 mm, astrength sufficiently resistant against a fastening force in the case ofstacked filters or a compressed load due to polymer pressure, that is, ahigh strength causing no deformation when applied with such a load canbe provided. Further, in a case where a high-strength material such as"CSPH" material is used, it is possible that an appropriate width isprovided to the slit itself (that is, a stripe portion having anappropriate width is cut away from the material), the pitch ofarrangement of the portions between the slits is enlarged and the pitchof respective supporting portions formed by being twisted at an angle of90 degrees is enlarged. In the case of a high-strength material, even ifthe pitch of arrangement of supporting portions is relatively large, asufficiently great pressure resistance can be provided.

In the above-described hub ring for a filter, the molten polymer 7 isfiltered by filter media 5, flows into hub ring 2 through the portion ofretainer 3, and is gathered in supporting pole 8 through a polymer path15 formed between a pair of keep plates 9a and 9b. Firstly, when theportion arranged with supporting portions 10a is viewed in the portionbetween keep plates 9a and 9b, the spaces other than supporting portions10a in this portion are all formed as the polymer path 15. Therefore, anextremely great opening ratio can be obtained as compared with theconventional structure with small holes. This opening ratio isdetermined from the thickness and pitch of supporting portions 10a andthe diameter at a position of radially inner edge of the arrangement ofthe supporting portions 10a. Although hub ring 2 must be designed so asto have a sufficient strength against deformation in consideration of acompression load applied to keep plates 9a and 9b, that is, a fasteningload applied to the hub ring 2 in a case where a plurality of filters 1are stacked, in the present invention, while a sufficiently highstrength against deformation even against a total fastening load higherthan 10 tons can be provided, an opening ratio greater than 40%,preferably greater than 45%, can be easily provided.

For example, in the supporting member 10 shown in FIG. 4, because thethickness of supporting portion 10a is 1 mm and the pitch of thearrangement of the supporting portions 10a is 2.5 mm, a great openingratio of about 71% can be realized. If the pitch of supporting portions10a is maintained as it is and the thickness of supporting portion 10ais changed to 0.6 mm, an extremely great opening ratio of about 83% canbe realized.

In the portion where annular plate portion 10b is positioned, althoughthe annular plate portion 10b blocks a part of polymer path 15 as shownin FIG. 2, because a plate merely extending annularly is only interposedin the polymer path 15, it does not cause a great resistance against thepolymer flow, and even in this portion, a great opening ratio can beeasily ensured.

For example, when the gap between a pair of keep plates 9a and 9b is 2.5mm and the thickness of annular plate portion 10b is 1 mm, a greatopening ratio of 60% can be realized. When the thickness of annularplate portion 10b is 0.6 mm, an extremely great opening ratio of 76% canbe realized.

The pressure loss when the polymer passes can be greatly reduced by sucha great opening ratio. Usually, in a filter apparatus, the life of afilter is determined by a rise of a filtration pressure (pressure atentrance of filter media) due to clogging of filter media, and when thefiltration pressure reaches a predetermined upper limit, the filter isexchanged. As described above, if the opening ratio is increased and thepressure loss at a position of the hub ring is greatly reduced, aninitial filtration pressure is extremely reduced, the time available foruse of the filter until reaching the above-described upper limit isincreased (that is, the cumulative total amount of the passing polymeris increased) and the life of the filter can be greatly extended.

Further, since supporting portions 10a extend perpendicularly to keepplates 9a and 9b and they receive a load applied between the keep plates9a and 9b most efficiently, they indicate a great pressure resistance.Therefore, it becomes structurally possible to design them so that theycan easily indicate a great pressure resistance against a fasteningforce greater than 10 tons. Further, if supporting member 10 isconstructed from a stainless steel as in this embodiment, whensupporting portions 10a are formed in the supporting member 10 asaforementioned, a particular work hardening of the stainless steeloccurs and the pressure resistance can be further increased.

Moreover, since the opening ratio can be to be great as aforementioned,there is no portion causing a polymer residence over the entire ares ofthe polymer path 15 of the hub ring 2. Namely, the whole amount ofpolymer can be smoothly passed through the polymer path 15 of the hubring 2. Because there occurs no polymer residence, degraded polymer isnot generated, a defect in a product such as a fish eye caused byflowing-out of the degraded polymer can be prevented as well as troublesin manufacture of the product due to flowing-out of the degraded polymercan be prevented.

Furthermore, in the hub ring 2 according to the present invention, themethod for manufacturing it can also be greatly simplified andfacilitated as compared with that in the conventional hub ring. Namely,in the hub ring 2 according to the present invention, keep plates 9a and9b and supporting member 10 can be processed separately, the keep plates9a and 9b, of course, can be easily manufactured at a large scale aswell as, even in supporting member 10, as shown in FIG. 6, becausemerely the processing for defining slits 12 on the annular plate and theprocessing for twisting the portions 13 between the slits 12 at an angleof 90 degrees may be performed, it can be easily processed as comparedwith the conventional structure having small holes. By combining thesemembers, a desired hub ring 2 can be easily completed. Therefore, thehub ring 2 can be manufactured easily, in a short period of time andinexpensively in a simple process.

When the pair of keep plates 9a and 9b and the supporting member 10 areassembled, for example, as shown in FIG. 7, these members may be fixedto each other at a predetermined positional relationship by welding suchas spot welding (welded portion 16). Thus, the hub ring 2 can be formedas an integrally formed part, and the handling thereof can be greatlyimproved.

Further, although a method for manufacturing a supporting member 10using an annular plate as a raw material plate has been explained in theabove-described embodiment, other methods may be employed. For example,as shown in FIG. 8, a plurality of slits 21 are defined on a straightplate 20 formed in a stripe-like shape, the portions positioned betweenthe slits 21 and the end portions positioned outside of both end slits21 are twisted at an angle of 90 degrees to form supporting portions,and thereafter, as shown by arrows, the plate member is bent to form aannular plate by bending in order to manufacture a supporting membersubstantially the supporting member as that shown in FIG. 4.

Furthermore, although the annular plate portion 10b is disposed on theouter circumferential side of the arrangement of supporting portions 10ain the above-described embodiment, this annular plate portion 10b may bedisposed on the inner circumferential side of the arrangement of thesupporting portions 10a. For example, in a supporting member 17 shown inFIG. 9, an annular plate portion 17b is disposed on the innercircumferential side of the arrangement of supporting portions 17aformed by twisting at an angle of 90 degrees.

Next, a supporting plate for a filter according to the present inventionwill be explained with reference to the drawings together with a methodfor manufacturing the same.

FIGS. 10 to 12 illustrate a supporting plate for a filter according toan embodiment of the present invention and a filter element using thesupporting plate. In FIG. 10, label 10 indicates the whole of a leafdisc-type filter element. Filter element 31 comprises a retainer 32disposed at a central position in the thickness direction of the filterelement, perforated plates 33 disposed on both surfaces of the retainer32 as filter media supporting material, filter media 34 disposed outsideof the respective perforated plates 33 and a hub ring 35 disposed on theinner circumference of the filter element 31. In a case where aplurality of filter elements 31 are stacked by a predetermined number,in this embodiment, spacers 36 having a predetermined thickness andformed as a member radially extending are disposed between respectiveadjacent filter elements 31 in order to ensure polymer paths between therespective adjacent filter elements 31. The molten polymer 37 to befiltered, as shown by arrows, is filtered by filter media 34. It thenpasses through perforated plates 33 and the portion of retainer 32, andit is gathered in a central supporting pole 38 after passing hub ring35, and thereafter, it is sent to a next process. Although the spacers36 are provided as separate members in this embodiment, hub ring 35 maybe constituted as a member having the spacer function.

In this embodiment, the retainer 32 is constructed as a supporting platefor a filter according to the present invention. FIG. 11 shows a patternof pressing for the retainer 32 (supporting plate for a filter) and FIG.12 shows an enlarged part of the supporting plate 32 pressed to astructure having wave forms, respectively.

In FIG. 11, black portions indicate portions each protruded and curvedas a convex portion as viewed from one surface side of the supportingplate 32. FIGS. 13 to 15 described later are illustrated in the samemanner.

A plurality of wave portions 39 are formed by pressing as follows.Namely, as shown in FIG. 12, a plurality of wave portions 39 eachextending substantially in a circumferential direction X--X of thefilter and waving in a thickness direction of the filter are formed bypressing so as to be arranged substantially adjacent to each other in aradial direction Y--Y of the filter. In this embodiment, the respectiveadjacent wave portions 39 are substantially connected to each other.Further, the wave forms of the respective adjacent wave portions 39shift in the circumferential direction X--X of the filter bysubstantially 1/2 pitch of one of the wave forms. This shifting of pitchis not particularly restricted, and a shift amount of, for example, 1/3pitch or 1/4 pitch may be set. In FIG. 12, "P" indicates one pitch ofthe wave form.

As shown in FIG. 11, a first group of wave portions 39 among theplurality of wave portions straightly are formed by pressing and theyextend substantially in the circumferential direction of the filter at aconstant angle relative to a radial direction of the filter passingthrough a center O (it is also a center of supporting plate 32) within afirst region A1 of the supporting plate 32 circumferentially divided ata predetermined circumferential angle. A second group of wave portionshaving the same pattern as that in the first region A1 are formed bypressing within a second region of the supporting plate 32circumferentially divided at a predetermined circumferential angle whichis adjacent to the first region in the circumferential direction of thefilter. This pressing is repeated in the circumferential direction ofthe filter and the wave portions 39 are formed over the entirecircumference of the supporting plate 32.

Although the circumferential angle of each region around center O can befreely set within the range of about 10 to 90 degrees, a circumferentialangle in the range of 20 to 60 degrees is preferred from the viewpointsof easiness of repeated pressing and easiness of manufacture of a diefor pressing. In FIG. 11, the angle is set at about 30 degrees.

In the pattern of the wave portions shown in FIG. 11, the pitch of thewave forms of the wave portions 39 is substantially constant over theentire wave portion forming area.

Further, in the pattern of the wave portions shown in FIG. 11, becausethe wave portions 39 are press-formed even on the boundary between therespective adjacent circumferential regions, a convex portion or aconcave portion contacting the boundary line is formed as a halfwaystyle. Although such a state is allowed and a wave portion reaching theboundary line or a wave portion formed near the boundary line can beconnected to a wave portion formed at the next adjacent circumferentialregion, there are the following methods in order to prevent therespective wave portions formed on the boundary line or the vicinitythereof of adjacent circumferential regions from interference.

Firstly, there is a method for providing a non-pressing band regionhaving an appropriately small width along the boundary line. As anothermethod, in a case where there occur convex or concave portions of waveforms over the boundary in a circumferential region, the convex orconcave portions of wave forms are allowed to extend into the nextadjacent circumferential region until the convex or concave portions arecompleted, and instead of this allowance, in the next adjacentcircumferential region, the forming of convex or concave portions to bepressed in the area of the above extended convex or concave portions isstopped, that is, in the next adjacent circumferential region, theforming of the wave portions are started from a position retreated fromthe boundary line by the amount of the above extension of the waveforms.

Another forming pattern is shown in FIG. 13. In this forming, in asingle circumferential region A1 in which wave portions are formed byone pressing using a die, the region A1 is further divided into tworegions B1 and B2, and in the divided regions B1 and B2, wave portions40a and 40b may be formed by pressing which are extended straightlysubstantially in the circumferential direction of the filter atdifferent angles to each other relative to the center O. In theembodiment shown in FIG. 13, although the respective wave portions 40aand 40b are formed so as to form "/\" pattern relative to center O, itmay be formed as a reversed "/\" pattern. By repeating the pressingusing such a pressing die, wave portions are formed on the successiveregion A2, . . . in order.

In such a pattern, the polymer flow passing through the region B1 andthe polymer flow passing through the region B2 in a singlecircumferential region A1 are naturally controlled in a symmetric andequivalent condition.

FIG. 14 shows a further forming pattern of wave portions.

In this embodiment, with respect to the pitch of the wave forms of thewave portions of a supporting plate 32, the pitch of the wave portions41a formed in the radially outer portion of the filter and the pitch ofthe wave portions 41b formed in the radially inner portion are differentfrom each other. Although the pitch of the wave portions 41b formed inthe radially inner portion is greater than the pitch of the waveportions 41a formed in the radially outer portion in this embodiment, itis possible to reverse the relationship of the sizes of the pitches.Further, although the pitch change is performed at two steps in thisembodiment, it is possible to set three or more steps.

In the portion of supporting plate 32 (the portion of retainer 32),because the polymer having passed through filter media 34 is gatheredfrom the radially outer side to the radially inner side as shown in FIG.10, the amount of the polymer becomes greater as the polymer flowapproaches the innermost side. Accordingly, by setting the pitch of thewave forms of the radially inner wave portions 41b greater, the width ofeach path formed by the wave forms of the wave portions 41b can be setgreat in the radially inner portion, and thereby suppressing theresistance against the polymer flow even if the amount of the polymerflow increases in the radially inner portion.

FIG. 15 shows a further forming pattern of wave portions.

In this embodiment, a plurality of wave portions 42 concentricallyextend in circumferential direction of the filter. In order to directthe polymer paths formed by the convex portions and the concave portionsof the respective adjacent wave portions 42 to directions toward thecenter O, the pitches of the wave forms of the wave portions 42 becomegradually small as approached to the center.

In such a forming pattern, the polymer flow can be directed precisely tothe direction toward the center O.

Further, the pattern can be formed by pressing using a plurality ofannular dies having diameters different from each other and forming thewave portions in order in the radial direction other than theaforementioned method wherein the respective circumferential regions arepressed in order in the circumferential direction. In this method, thewave portions may be formed one row by one row using the respectivedies, or the wave portions may be formed by several sets of rows.

Further, as shown in FIG. 16, a portion 44 present between two waveportions 43, 43 substantially adjacent to each other in the radialdirection Y--Y of the filter remains as a portion which does not wave.This portion 44 which does not wave extends circumferentially as a bandhaving a small width. The width of the portion 44 is preferably in therange of 1 to 3 mm.

The press-forming of the wave portions 43 to predetermined forms can befurther facilitated by providing such portions 44.

Furthermore, when the wave portions are press-formed in the aboverespective embodiments, although they may be formed only by pressing, itis preferred that a plurality of slits are defined intermittently in thecircumferential and radial directions of the annular plate for formationof a supporting plate by, for example, etching, and portions betweenrespective pairs of slits are formed as the wave portions by pressing.Namely, preferably a pressing die functions only for providing waveforms. The wave portions can be formed at a higher accuracy by such aforming method.

Although various press-forming patterns for the wave portions can beemployed as described hereinabove, the operation and advantages withrespect to the embodiment shown in FIGS. 10 to 12 will be explained.

As shown in FIG. 12, polymer paths extending in the radial directionY--Y are formed by the adjacent convex portions and concave portions ofthe wave portions 39 radially adjacent to each other at 1/2 pitchshifting. The polymer filtered by filter media 34 and having passedthrough filter media supporting material 33 easily flows into thesupporting plate 32 from upper and lower sides as shown by arrows.Thereafter, the polymer flows easily and smoothly along the polymerpaths extending in the radial direction formed as described above. Sinceresistance against this polymer flow in the radial direction is only theportion corresponding to the thickness of the supporting plate 32, agood directability can be provided in the above direction along thepolymer paths as well as the pressure loss can be suppressed as comparedwith that in the structure shown in FIG. 22. For example, in a casewhere the thickness of a supporting plate is designed to be 2.5 mm, inthe present invention, it is sufficient to use a raw material platehaving a thickness of 0.5 to 0.7 mm, but in the conventional structureemploying a wire mesh, it is necessary to use a wire having a diameterof 1.3 to 1.5 mm. Therefore, in the present invention, the ratio of thedead volume to the total thickness can be suppressed extremely small.

Further, as shown by arrows in FIG. 12, the polymer flows along thepolymer paths in the radial direction are divided and can freely flowinto and out between adjacent polymer paths. The polymer flows freelyinto and out between adjacent polymer paths provide an excellent staticmixer effect, and the polymer can be naturally and uniformly mixedduring gathered toward the supporting pole 38 through the supportingplate 32. Further, if the pitch for shifting adjacent wave portions isset to 1/3 pitch or 1/4 pitch, a further excellent static mixer effectcan be obtained.

Furthermore, the convex portions and concave portions of the wave formsof a plurality of wave portions 39 are arranged in a staggered form asshown in FIG. 11, and a portion constituting a convex portion as viewedfrom one surface side forms a concave portion as viewed from the othersurface side. Namely, the convex portions are arranged in a staggeredform on both surface sides. These convex portions protruding from bothsurfaces can provide a required thickness to the supporting plate 32 aswell as can form surfaces for supporting filter media supportingmaterials 33 disposed on both surface sides of the supporting plate.

In the wire mesh type retainer 102 shown in FIG. 22, because each wavingwire comes into contact with each filter media supporting material 103substantially at a point contact, the local stress generated in thecontact point is high. On the contrary, in the present invention,because each wave portion waves and has a width, the contact state witheach filter media supporting material 33 is nearly line contact.Therefore, the local stress can be greatly reduced as compared with thestructure shown in FIG. 22. The wave portions can hardly be deformed bya pressure loaded from upper and lower sides and can indicate anextremely high pressure resistance.

The convex portions of each wave portion 39 can indicate a high pressureresistance and the convex portions are arranged in a staggered form asshown in FIG. 11. Therefore, an extremely high pressure resistance canbe indicated also as the whole of the supporting plate 32.

Further, since a plurality of wave portions 39 are formed by pressingand adjacent wave portions 39 are integrally connected to each other atany portion of the wave form, the respective wave portions 39 supplementeach other in strength, thereby indicating a further high pressureresistance as the whole of the supporting plate 32.

In the press-forming patterns shown in FIG. 11 and FIGS. 13 to 15, amethod for forming a predetermined pattern in order on thecircumferential regions A1, A2, . . . and forming the supporting plate32 as a integrally formed member provided with wave portions over theentire circumference is shown. However, because the supporting plate 32prepared as a retainer is disposed inside of the filter element 31, itis possible to divide it in the circumferential direction into aplurality of members. For example, it is possible to make thecircumferential regions A1, A2, . . . as separate sector members anddispose these separate sector members to complete an annular plate form.

Further, although the supporting plate 32 is used as a retainer disposedat an innermost position of the filter element 31, it is possible to useit as a filter media supporting and retainer member. For example, asshown in FIG. 17, it is possible that filter media 34 are supporteddirectly on both surfaces of a supporting plate 50 prepared as a filtermedia supporting and retainer member, and the member has both functionsas a filter media supporting member and a retainer. Namely, since thesupporting plate for a filter according to the present invention has anextremely high pressure resistance as well as has a surface form whereina number of convex portions of the wave forms having a relatively broadcontact area are densely arranged, it is possible to form an apparentflat surface having a good flatness as viewed as the whole of thesupporting plate, thereby providing both functions of a filter mediasupporting member and a retainer to the supporting plate.

Further, the supporting plate for a filter according to the presentinvention can be combined with the aforementioned specified hub ringhaving a low pressure-loss property or can be formed integrally with thehub ring.

FIG. 18 shows a filter 60 in which the supporting plate 32 according tothe present invention is combined with a hub ring 61 similar to thatshown in FIG. 1. In FIG. 18, hub ring 61 comprises a pair of keep plates62a and 62b disposed spacedly from each other and each formed as anannular plate, and a supporting member 63 disposed between the pair ofkeep plates 62a and 62b and extending annularly. In the supportingmember 63, a plurality of supporting portions 63a each extending betweenthe pair of keep plates 62a and 62b and each extending in the radialdirection of the hub ring are arranged in the circumferential directionof the hub ring at an appropriate pitch. The plurality of supportingportions 63a are connected to an annular plate portion 63b at a positionof the outer circumferential side of the annular arrangement of thesupporting portions 63a. Label 64 indicates a spacer disposed betweenstacked hub rings.

Such a hub ring can be manufactured in a manner similar to thataforementioned, and the advantages aforementioned can be obtained in theportion of the hub ring. Further, this hub ring portion can beintegrally formed with a supporting plate according to the presentinvention. Namely, since a desired material is stainless steel for bothmembers, using an annular raw material plate composed of stainlesssteel, for example, as shown in FIG. 19, the supporting plate 32 and thesupporting member 63 of the hub ring can be integrally formed as anintegral plate 70. In FIG. 19, the supporting member 63 comprisingsupporting portions 63a and annular plate potion 63b is integrallyformed at the inner circumferential portion of the supporting plate 32having wave portions 39. The wave portions 39 can be formed by pressingand the supporting portions 63a can be formed by twisting at an angle of90 degrees, respectively, as aforementioned.

By such a integral forming, the number of the parts for a filter elementcan be reduced as well as the handling of the filter element, theassembly of the filter element and the stacking construction of aplurality of the filter elements can be facilitated.

Further, also the keep plates 62a and 62b can be substantiallyintegrally constituted by welding them to the supporting member 63,thereby further improving the properties on assembly and handling.

FIGS. 20 and 21 show a supporting plate for a filter according toanother embodiment of the present invention and a method formanufacturing the same.

In this embodiment, as shown in FIG. 20, a plurality of slots 82extending in a radial direction Y--Y of an annular plate 81 are definedon the annular plate 81 and arranged in the circumferential directionX--X of the annular plate 81. The annular arrangement rows are disposedin plural in the radial direction Y--Y of the annular plate 81. Theportions 83 positioned between respective adjacent slots 82 are twistedsubstantially at an angle of 90 degrees relative to the upper and lowersurfaces of the base plate portion of the annular plate 81 to form riserpiece portions 84 rising perpendicularly from upper and lower surfacesof the base plate portion of the annular plate 81 at an angle of 90degrees (FIG. 21). The riser piece portions 84 thus formed are arrangedin plural in the circumferential direction X--X and the radial directionY--Y to form a supporting plate 85 for a filter.

In this embodiment, each slot 82 has circular holes 82b at both endportions in its longitudinal direction, the circular holes 82b have adiameter greater than a width of a central portion 82a of the slot, andby this structure, twisting for forming the riser piece portions 84 canbe facilitated. However, such circular holes 82b are not necessary, anda slot merely having a constant width substantially over the entirelength may be employed. Further, instead of the slots, slits may beemployed.

Furthermore, in a case where the riser piece portions 84 are arrangedconcentrically on the supporting plate 85, a ring portion 86 of the baseplate portion of the supporting plate 85 positioned between radiallyadjacent rows of riser piece portions 84 may be waved in the thicknessdirection of the base plate portion. In this case, it is preferred thatthe heights of the riser piece portions 84 from the upper and lowersurfaces of the base plate portion of the supporting plate 85 aresubstantially the same as the heights of a wave form of the ring portion86 from the upper and lower surfaces of the base plate portion. By sucha structure, the strength of the supporting plate 85 can be furtherincreased, and even when the riser piece portions 84 are formed bytwisting, undesired deformation of the ring portion 86 can be prevented.

In this type of supporting plate 85, stainless steel is preferred as araw material. Further, the supporting plate 85 can be assembled with theaforementioned hub ring and, further, both members can be integrallyformed.

Using such a type of supporting plate having a plurality of riser pieceportions, a filter having low-pressure loss and high pressure resistanceproperties and a high performance can be realized.

Although several preferred embodiments of the present invention havebeen described in detail herein, the invention is not limited thereto.It will be appreciated by those skilled in the art that variousmodifications may be made without materially departing from the noveland advantageous teachings of the invention. Accordingly, theembodiments disclosed herein are by way of example. It is to beunderstood that the scope of the invention is not to be limited thereby,but is to be determined by the claims which follow.

What is claimed is:
 1. A method for manufacturing a supporting plateprovided inside of a disc-type filter comprising:forming an annularplate having opposed surfaces; and forming a plurality of longitudinallyextending wave portions in said annular plate by pressing, which waveportions alternately extend beyond said opposed surfaces in oppositedirections, each of said plurality of wave portions extendingsubstantially in a longitudinal circumferential direction of saidannular plate and said plurality of wave portions being arrangedsubstantially adjacent to each other in a radial direction of saidannular plate.
 2. The method for manufacturing a supporting plateaccording to claim 1, wherein a first group of wave portions is formedby pressing on a first region of said annular plate circumferentiallydivided at a predetermined circumferential angle, a second group of waveportions is formed by pressing on a second region of said annular plateadjacent to said first region in the same pattern as that in said firstregion, and additional groups of wave portions are formed substantiallyover the entire circumference of said annular plate.
 3. The method formanufacturing a supporting plate according to claim 1, wherein saidplurality of wave portions are formed by using a plurality of annulardies having diameters different from each other.
 4. The method formanufacturing a supporting plate according to claim 1, wherein aplurality of slits are defined intermittently in the circumferential andradial directions of said annular plate, and portions between respectivepairs of slits are formed as said wave portions by pressing.